The invention pertains to a knotting hook and to a twine knotter equipped therewith.
Twine knotters of this type have been known for many years under the name “McCormick system” and are described on pages 128-131 of the book “Landmaschinenlehre” [Textbook of Agricultural Machinery”], Vol. II, by Prof. Heinrich Heyde, Dr. Eng. (editor), VEB Verlag Technik Berlin, Berlin 1965.
Twine binders or twine knotters of this type are used in bale compactors for straw, hay, and similar materials and also in the recycling field, for example, to tie up bundles of paper, textiles, thin sheets of metal, and the like. Twine binders are also used in machines for tying small bundles of stalky material with twine. “Stalky material” in this case consists primarily of agricultural or horticultural products such as leeks, onion necks, grafting understock, flowers, individual plants with their branches such as rose bushes, etc. Binding machines or binding devices of this type, however, can also be parts of packaging systems for typing packages, bales, and bundles of materials suitable for being tied into bundles.
In stationary or mobile compactors, the material in question is packed into a compaction channel with a rectangular cross section. Block-like units, also called bales, are sectioned off from the rectangular strand of compacted material; these bales are then wrapped with binding twine in planes parallel to the direction of the channel. Before the bale is ejected from the compaction channel, the twine is knotted to form a closed loop. In the case of simple built-in knotters, the strand of twine is cut off from the knot and clamped in position until the next wrapping operation. When double knotters are used, the two strands of twine are clamped only during the period between the tying of the first and the tying of the second knot. The processes of knotting, cutting off, and clamping are handled by the twine knotter.
Depending on the width of the block-like bale and the pressure prevailing inside it, one or more twine knotters are mounted next to each other on a common drive shaft in the compactor. The number of knotters and the number of compactor components which supply the strands of twine, namely, the so-called compactor needles, are determined by the number of times the bale must be wrapped with twine.
The drive shaft is located either above or below the essentially horizontal compaction channel. If the compaction channel is in another position, the drive shaft is mounted alongside it.
If a simple knotter is installed, the compactor needle guides the length of twine required to loop around and to tie the bale to the twine knotter, the twine thus being carried around behind the block-shaped bale, which has been cut off behind the compactor piston, which moves back and forth in the longitudinal direction of the compaction channel. After reaching the knotter, the twine is laid over the tongue of the knotting hook and carried further onward to the twine clamping device. From the latter, the end of the previously mentioned strand proceeds over the knotting tongue to the reversing edge of the knife lever and from there passes around the entire bale. If a double knotter is installed, both the part of the strand passing over the top and also the part of the strand extending along the bottom of the bale are conveyed by the compactor needle over the tongue of the knotting hook to the twine clamping device.
In the case of binding machines of the type described above, the material to be tied into a bundle is placed on a work table, which can be either horizontal or slanted. A crescent-shaped knotting needle guides the strand of twine around the bundled material, so that the end which is being held tightly in the knotter and the stand which has been wrapped around the bundle meet each other in the knotter, so that the knot can then be tied.
So that a complete and lasting knot can be tied, the knotting tongue, which is mounted pivotably on the knotting hook and which cooperates with the hook part of the knotting hook to form the so-called “knotting jaws”, must rest firmly on the hook part of the knotting hook before the knotting procedure is begun, or, expressed in different words, the knotting jaws must be kept closed. For this purpose, a spring-loaded closer presses against a tongue roller, which is rotatably supported at the rear of the knotting tongue. When the knotting hook rotates once around itself to form the loops of the knot, the roller of the knotting tongue is guided over a curved track, so that the knotting jaws, which are still closed at this point, open up just before the hook completes its rotation. The jaws open just enough to allow the two strands of twine, which are being held under tension between the twine holder and the knotting hook, to slide between the knotting jaws. After the hook has rotated a complete 360°, the jaws close again. The two previously mentioned strands are cut by the knife attached to the knife lever, and the knot loops formed by the knotting hook are stripped off the cut ends of the strands by the stripping comb of the knife lever. A loose knot is thus obtained, which acquires its final state as a strong, tight knot after completion of the stripping process by the action of the tensile force exerted by the material which has been compacted and tied and which keeps trying to expand outward again.
The adjustable pressure which the closer applies to the tongue roller will vary as a function of the weight of the bale and thus also on the thickness of the required compacting twine. The designs of the knotting hook, of the knotter tongue, and of the associated tongue roller will also vary as a function of the thickness of the twine.
Shortly before the rotation of the knotting hook, as already mentioned, the two strands to be knotted together lie on the tongue of the knotting hook. The knotting jaws are kept closed by this contact pressure and by the pressure being applied by the closer to the tongue roller. A continuous closing pressure is also exerted on the knotting jaws during the rotation of the knotting hook.
The knotting tongue, which passes through a rectangular opening in the head of the knotting hook, is supported with freedom to pivot on a pivot pin in the knotting hook. This pin consists either of solid material (a straight pin) or of a piece of wound sheet metal (dowel sleeve, spiral pin). By suitable selection of the bore tolerances, this pin can be held in the knotting tongue so that the ends of the pin can rotate in the two cheeks at the sides of the rectangular opening in the head of the hook, or the pivot pin can be fixed in position in the previously mentioned cheeks, so that the knotting tongue can rotate around it.
As a result of the tension exerted by the compacting twine and/or the force of the closer, the load which acts on the pivot pin can be considerable. Use in the field has shown that these loads can occasionally cause the pivot pin to slide in the axial direction until it projects out laterally from the head of the hook. The strands which have been looped around the head of the hook during the knotting operation can thus be damaged, and this can lead in turn to a significant decrease in the strength of the knot, which sometimes remains unnoticed when the knotter is being operated continuously.
The axial displacement of the pivot pin can be caused by: high compaction densities, which increase the tension in the twine to be knotted to such an extent that the resulting forces acting via the tongue can exert a damaging effect on the fitted seat of the pivot pin; an unfavorable combination between the manufacturing tolerances for the pin and those for the bores into which it fits; the dimensions of the pin and of the bores or their manufacturing tolerances are inconsistent and therefore imprecise; and, the failure to properly maintain the specified strength or hardness values of the pivot pin.
It is known that the axial displacement of the pivot pin can be prevented by designing the receiving bore in one of the cheeks of the knotting hook as a blind hole, that is, as a hole which is closed off by a wall at the bottom.
After the pivot pin has been pressed into place to a point just in front of the bottom of the bore, the edge around the bore in the opposite cheek of the opening is peened over in front of the end surface of the pivot pin located there in order reliably to secure the pivot pin in position.
This method of securing the pin suffers from the disadvantage that the knotting tongue cannot be removed after it has become worn out or damaged, because the bottom of the blind hole blocks off the end of the pin, which means that there is no place where a driver could be put to knock out the pin.
Thus, there is a need for knotting hook with a removable pivot pin. Even though the pivot pin is prevented from sliding out of place in the axial direction, it can nevertheless be removed with the help of driver when repairs are needed.